Two rotating discs

1. The problem statement, all variables and given/known data
A disk of mass M1 = 350 g and radius R1 = 10 cm rotates about its symmetry axis at f initial = 151 rpm. A second disk of mass M2 = 251 g and radius R2 = 8 cm, initially not rotating, is dropped on top of the first. Frictional forces act to bring the two disks to a common rotational speed f final.
In the process, how much kinetic energy is lost due to friction?

3. The attempt at a solution
Given that I have an equation and data to punch in, this should be really simple. However, to reconcile the fact that there are two radius' in the final solution, I decided to calculate KE for each disc separately. That is correct, right?
Anyways, here goes:
Initial K:
1/2 I W^2 + 1/2 mv^2
1/2 1/2 mr^2 151^2 + 1/2 m (Wr)^2
1/4 35,000 22801 + 1/2 350 2280100
199508750 + 399017500
Initial K = 598526250